accumulate的意思是积累,这里理解为延伸
全句的意思是一本经典就是无论你读不读它的时候,它的意思都能得到延伸,我觉得意思是有点举一反三和授人渔的意思
which accumulates its meanings whenever it is being read修饰前面的a book,说明此书怎样才能成为经典,whenever修饰说明which的时间
至于例句嘛,我想了一个：A hard-working student is someone who will study hard no matter whether his teacher is beside him.